VIMS team studies aftermath of Alaskan “Snowpocalypse”

Snow HouseSo much snow fell during southeastern Alaska's 2012 "Snowpocalypse" that the National Guard had to free people trapped in homes and businesses.
Image courtesy of Jim Wessel.

Copper River PlumeThe sediment-laden waters of the Copper River are clearly visible even far out to sea.
Photo courtesy of Professor Steve Kuehl.

X-Ray FluorescenceThe research team dated and analyzed their sediment cores using a cutting-edge XRF analyzer at Texas A&M University.
Photo courtesy of Professor Steve Kuehl.

Copper River PlumeA satellite image shows how sediment-laden discharge from the Copper River forms a plume that is carried into nearby Prince William Sound.
Image courtesy of NASA.

Snowfall RecordGraph of December‐February snowfall totals for Copper River area since 1950 shows that the January 2012 snowfall event is the largest on record. Vertical scale is meters of snow.
Image courtesy of Prof. Steve Kuehl.

Coring of seafloor sediments may give
long-term record of changing Arctic climate

In January of last year, a series of epic snowstorms struck
Alaska’s panhandle, leaving up to 18 feet of snow in many areas. That’s six
times more snow than fell during the blizzard that paralyzed New England in
early February.

Professor Steve Kuehl of the Virginia Institute of Marine
Science, College of William & Mary, is now awaiting word on a proposal to further investigate whether river
runoff from this so-called "Snowpocalypse" left a signature in nearby
seafloor sediments, and if so, what the long-term record of such events might
say about the area's fast-changing climate.

“We talk about climate change and extreme weather events,”
says Kuehl, “but what happened in this case was over the top, even for an area
of Alaska that’s used to heavy snows. They had to call out the National Guard
to get people out of their houses in Cordova—it was extraordinary.”

Kuehl’s study, initially funded by a “Rapid Response” grant
from the National Science Foundation, builds on seminal work by fellow VIMS
Professor John Milliman. Milliman’s research has shown that small mountain
rivers—such as the Copper River that drains southeast Alaska’s Chugach and
Wrangell mountain ranges—carry a disproportionate amount of sediment to the
global ocean.

“The Copper River discharges about 70 million tons of
sediment to the ocean every year,” says Kuehl. “That’s almost 20 percent as
much as the Mississippi, even though the Mississippi’s drainage basin is 50
times larger.” Local currents carry much of the Copper’s heavy sediment load into
nearby Prince William Sound, where earlier work by Milliman and other
researchers reveals the accumulation of an astounding 450 feet of sediment
during the last 10,000 years.

As its name implies, NSF’s Rapid Response program provides
an opportunity for scientists to quickly compete for the funds needed to
investigate the causes and impacts of ephemeral events such as storms,
earthquakes, and tsunamis—condensing a proposal process that typically take
months into a few weeks.

“We successfully submitted a Rapid Response proposal in
spring 2012 and used the funds to look at the hydrology of the river during last
year’s spring melt,” says Kuehl. “We first wanted to see what effects the
melting of the heavy snowpack would have on the coastal ocean— to characterize
the river’s plume. We also wanted to collect sediment cores to see if we could identify
proxies for Copper River discharge that we might eventually be able to tie back
to long-term climate patterns.”

Kuehl notes that last year’s unprecedented snowfall in
southeastern Alaska—twice that previously measured for December through
February since records began in 1950—was related to the northerly position of
the jet stream and a stationary Aleutian low-pressure system. These factors also
contributed to record winter warmth throughout the lower 48 states, and have been
cited as a harbinger of present and future climate change.

“Climate drivers such as the Arctic Oscillation, Pacific Decadal
Oscillation, and El Niño Southern Oscillation have likely influenced the past
positions of the Aleutian Low, and hence year-to-year variations in Copper
River discharge,” says Kuehl. “Understanding the relative importance of last
year’s event in the context of past changes driven by these climatic
oscillations will require the development of paleo-proxies of Copper River discharge,
which our early results suggest are preserved in the rapidly accumulating
sediments of Prince William Sound.”

A proxy is a chemical or physical attribute—like the width
of a tree ring—that can be used to track changes in some other environmental
variable—like precipitation—on a periodic, often annual, basis. Retrieved by
coring into sediments, ice, corals, or other materials, paleo-proxies extend knowledge
of environmental changes back through geologic time.

Kuehl says that areas where sediments accumulate rapidly,
like Prince William Sound, are favored for proxy studies because they’re more
likely to hold a detailed record of past changes. “It’s like the difference
between an image taken by a cell phone versus a high-end camera,” he explains.
“The higher the data or sedimentation rate, the clearer the picture.”

Developing a paleo-proxy requires dating the sediments in a
core, which Kuehl’s team did using various naturally occurring radioisotopes
such as Pb-210, which has a half-life of 22.3 years. “We analyzed lead-210
activity with depth in a 5-foot core taken near the mouth of Prince William
Sound,” says Kuehl, “and came up with an accumulation rate of about 6 centimeters
per year, which is pretty phenomenal.”

Even more exciting was their discovery of distinct layers in
the core, which they suspect may signal the annual spring melt. “If there’s a
place where we can develop a high-resolution proxy for Copper River discharge,”
says Kuehl, “I think we have an opportunity here.”

The team analyzed their cores using a cutting-edge technique
called X-ray fluorescence. “The beautiful thing about XRF,” says Kuehl, “is that
you get a read-out of age and elemental concentrations all at once, and at very
high resolution down the core. The elemental composition is tied back to the
geology of the surrounding basins, with significant differences between the
Copper River watershed and the area to the north. We hope we can take advantage
of those differences to identify the annual signal of Copper River runoff into
Prince William Sound.”

The team’s analysis revealed one more intriguing discovery—a
disturbed section within several cores that the researchers think might record Alaska’s
1964 Good Friday Earthquake, the second largest earthquake ever measured.

“Our initial thought,” says Kuehl, “was that the sediments
of Prince William Sound might record the history of Copper River discharge and
how it might be influenced by climate. But now we think those sediments may
also contain an unparalleled seismic record extending back 10,000 years. We’re
hoping to get back up to Alaska as early as this summer to take longer cores
for additional analyses.”